Interestingly, the 28-year-old had a working relation when the Spaniard spent two years as Porto manager, and Herrera is reportedly set to join the big spenders soon.

However, the duo of Paris Saint-Germain and Barcelona are equally keeping vigil, even as Arsenal and Roma have also being linked with the highly-talented midfielder.

Italian news channel, Corriere dello Sport suggests that the clubs, who are eyeing Herrera, are likely to move for him in the winter window ahead of a potential Bosman switch, before the 2019-2020 campaign.